Purpose: To investigate the effect of two different smear layer thicknesses treated with different dentin conditioners on the bond strength of glass-ionomer adhesive to dentin. Materials and Methods: Fifty human molars were used. Each tooth was sectioned in a mesiodistal direction into halves, using a low-speed diamond disk. The 100 halves were randomly divided into 10 equal groups. Groups I to V for the thick smear layer and groups VI to X for the thin smear layer. Eighty halves were used for shear bond strength testing, while the remaining 20 halves were used for SEM evaluation of the adhesive/dentin interface. After each dentin pretreatment, the glass-ionomer adhesive was applied over the conditioned dentin surfaces for all tested groups and restored with resin composite cylinders. Each half with its attached composite cylinder was subjected to shear load at crosshead speed of 0.5 mm/min until failure occurred. The dentin surfaces for SEM evaluation were treated as described for shear bond strength testing. The samples were examined using SEM operated at 30 kv, and the resin/dentin interface was examined at 1500X. Results: Two-way ANOVA showed that there was no significant effect of the smear layer thickness on shear bond strength. There was a significant effect of the different conditioners used (p = 0.001). The interaction of the two independent variables (smear layer thickness and the dentin conditioners) showed no significant difference in the shear bond strength to dentin. The common feature in all evaluated specimen interfaces was the presence of a hybrid layer of different thicknesses with no visible resin tags. Conclusions: The shear bond strength of the glass-ionomer adhesive to dentin proved to be independent of the smear layer thickness. The use of dentin conditioner prior to the application of the glass-ionomer adhesive appeared to be an important step to improve its bond strength to dentin. Glass-ionomer adhesive failed to produce resin tags regardless of the type of dentin conditioner used.